Assign a formal charge to each atom of ClO
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The Correct Answer and Explanation is:
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Correct Answer
c. Cl = 2+; O = 1-
Explanation
To determine the formal charge on each atom in the chlorate ion (ClO₃⁻) for the given Lewis structure, we use the following formula:
Formal Charge = (Valence Electrons) – (Non-bonding Electrons) – ½(Bonding Electrons)
Let’s apply this formula to each atom in the provided structure.
1. Formal Charge of Chlorine (Cl):
- Valence Electrons: Chlorine is in Group 17 of the periodic table, so it has 7 valence electrons.
- Non-bonding Electrons: In the given Lewis structure, the chlorine atom has one lone pair, which consists of 2 non-bonding electrons.
- Bonding Electrons: The chlorine atom is forming three single bonds (one with each oxygen atom). Each bond has 2 electrons, so there are 3 × 2 = 6 bonding electrons associated with chlorine.
Now, we calculate the formal charge for Cl:
Formal Charge (Cl) = 7 – 2 – ½(6)
Formal Charge (Cl) = 7 – 2 – 3
Formal Charge (Cl) = +2
2. Formal Charge of Oxygen (O):
The Lewis structure shows three identical oxygen atoms. Each oxygen atom has one single bond and three lone pairs. We only need to calculate the formal charge for one of them.
- Valence Electrons: Oxygen is in Group 16, so it has 6 valence electrons.
- Non-bonding Electrons: Each oxygen atom has three lone pairs, which total 3 × 2 = 6 non-bonding electrons.
- Bonding Electrons: Each oxygen atom forms one single bond with the central chlorine atom, which consists of 2 bonding electrons.
Now, we calculate the formal charge for O:
Formal Charge (O) = 6 – 6 – ½(2)
Formal Charge (O) = 6 – 6 – 1
Formal Charge (O) = -1
Conclusion and Verification:
The formal charge on the chlorine atom is +2, and the formal charge on each of the three oxygen atoms is -1.
To verify our results, the sum of the formal charges of all atoms in the ion must equal the overall charge of the ion, which is -1.
Sum of Formal Charges = (Formal Charge of Cl) + 3 × (Formal Charge of O)
Sum of Formal Charges = (+2) + 3 × (-1) = 2 – 3 = -1
The sum of the formal charges is -1, which matches the overall charge of the ClO₃⁻ ion.
Therefore, the correct assignment of formal charges is Cl = 2+ and O = 1-.
